The present invention relates to an improvement in processes for the recovery of uranium in the uranyl form from solutions. The invention is particularly applicable to processes for the recovery of uranium from wet process phosphoric acid like that disclosed in U.S. Pat. No. 3,835,214. In the process of the patent the uranium is recovered from a phosphoric acid solution resulting from the treatment in the wet process plant of phosphate ore with sulfuric acid to make fertilizer. The feed solution is a phosphoric acid solution containing sufficient uranium to warrant its recovery. In the first liquid-liquid solvent extraction circuit of the process the uranium in the phosphoric acid solution is reduced to uranous form and recovered from the phosphoric acid feed solution on a solvent extraction agent for reduced uranium, and the uranium recovered from the loaded agent by an oxidative strip with phosphoric acid. The uranium in uranyl form is recovered from the strip solution with DEHPA-TOPO liquid-liquid solvent extraction agent and stripped from the agent with ammonium carbonate to form ammonium uranyl tricarbonate which is calcined to form the product uranium oxide. The present invention is applicable to the second stage strip and uses an alkali metal carbonate rather than ammonium carbonate as a stripping agent, all as disclosed in our copending U.S. patent application, Ser. No. 833,247, filed in the U.S. Patent and Trademark Office on Sept. 14, l977.
In processes for stripping uranyl uranium from ion exchange agents like DEHPA as disclosed in the above-mentioned patent, ammonium carbonate is conventionally used as a stripping agent. Prior to the stripping, the loaded agent is conventionally scrubbed with water. Also, after the liquid-liquid solvent extraction agent is stripped with ammonium carbonate, the agent is conventionally recycled to the extraction step using DEHPA without regeneration or purification.
It has been noted that water scrubbing the DEHPA-TOPO agent in the second circuit of the patent before stripping does not adequately remove such impurities as phosphorus, iron, and vanadium. Use of an ammonium carbonate strip of the oxidized uranium from the agent results in the precipitation of uranium in the strip concentrate solution, thus causing solids accumulation in the strip circuit, and introduces the problem of organic wetting of the yellow cake product.
Recycling of the stripped organic of the second circuit without regeneration presents phase separation problems resulting from emulsions formed with sodium, aluminum, and silicon.
Accordingly, it is a principal object of this invention to provide a process for the recovery of uranyl uranium from solutions by liquid-liquid solvent extraction which eliminates the problems of the prior art set forth above.